Computer disk drives typically incorporate retrieval and storage of data by use of magnetic storage disks and read/write heads which are capable of reading data from and writing data onto the rotating storage disks. Data is stored on each magnetic storage disk in a number of concentric tracks on the disk. The narrower the tracks can be made, the more data which can be stored on the storage disk. The read/write heads may also be referred to as the read/write transducers which are integrated within a slider which typically places the heads at a predetermined height above the corresponding storage disk. One or more read/write heads may be integrated within a single slider. A suspension assembly supports the slider over the disk and maintains the slider over the desired data track center line during a read or write operation. A cushion of air is generated between the slider and the rotating disk, the cushion often referred to as an air bearing. The suspension assembly is part of the actuator which is the component in the disk drive for positioning the read/write heads. The actuator is typically controlled by a voice coil motor which acts as a primary actuator for positioning of the slider over the desired track. Because of the trend in recent years to provide greater storage capacity on a storage disk, track widths have become increasingly narrower which makes it more difficult for the read/write heads to accurately read and write information to and from the magnetic disks. The actuator has limited ability to accurately position a slider across the data tracks. Accordingly, a need has arisen over the years for the ability to more accurately position the read/write heads on tracks of decreasing width. As track density increases, the speed or servo bandwidth with which an actuator can respond must also increase to allow effective track following.
One approach to achieving finer positioning of the actuator is to employ secondary actuation that operates together with primary actuation provided by the voice coil motor. Secondary actuation can be provided in the form of an additional actuator control element which provides for finer control of the flexure and/or load beam. These additional control elements have often been termed “micro” or “milli” actuators.
It is known to utilize piezoelectric materials to achieve secondary actuation in a milli-actuator. The U.S. Pat. No. 6,404,600 discloses a prior art milli-actuator which may utilize two piezoelectric actuators mounted between the base plate of an actuator arm and load beam of an actuator. A narrowed section may be provided between the base plate and load beam, or the base plate and load beam may be physically separated. The piezoelectric elements act in a “push-pull” manner to move the load beam relative to the base plate. The distal end of the load beam carries the flexure and slider. Secondary actuation is therefore achieved by movement of the load beam which in turn moves the flexure and slider. This reference also discloses a pair of bimorph-actuators which are deflectable together in a common direction and which interconnect an inboard portion and an outboard portion of an actuator arm. Upon deflection of the bimorph-actuators in the same direction, the outboard portion of the actuator arm is translated along a path that is transverse to the longitudinal axis of the inboard portion. This transverse motion results in secondary actuation and further allows the read/write head to be kept substantially within a plane parallel to the surface of the data storage disk thereby preventing potential damage caused by possible contact between the slider and the disk surface.
Another reference disclosing a means of secondary actuation is the invention disclosed in U.S. Pat. No. 6,239,947. This reference teaches a milli-actuator having an integrated milli-actuator/electronics module which is positioned between the suspension of an actuator arm and the slider. The milli-actuator is an electrostatic rotary device in which a rotor structure is controllably rotated by the electronics module to provide the secondary actuation. Integration of the milli-actuator electronics with the milli-actuator reduces parasitic loading and interference problems with magnetic transducer signals.
Yet another example of a reference disclosing secondary actuation is the U.S. Pat. No. 5,657,188. In this reference, a micro-actuator is located on the load beam which controls movement of the flexure and the read/write heads attached to the flexure thereby achieving greater positional control of the read/write head on a desired disk track. The micro-actuator includes a moving pole member mounted to the flexure, a stationary pole member mounted to a rigid region on the load beam adjacent to the moving pole, and coils positioned around the stationary pole member.
While the above inventions may be adequate for their intended purposes, one particular drawback to previous micro/milli-actuator designs is that the secondary actuator mechanism actuates not only the slider, but also the load beam and/or the flexure. With the micro-flexure suspension of the present invention, only the slider is moved. The isolation of movement at the slider lowers the moving mass of secondary actuation, reduces windage excitation, and improves overall dynamic performance of the actuator. Windage excitation refers to some increase in loss of control over the read/write heads due to an increase in uncontrolled movement of the suspension due to airflow forces acting upon the suspension during operation. Incorporating a micro-actuator across the load beam and/or flexure may reduce the stiffness of the load beam and flexure and may contribute to uncontrolled suspension movement. Accordingly, any gain in fine positioning of the actuator by use of a micro-actuator may be lost by inability to minimize windage excitation.
Therefore, it can be seen that there is a need to provide secondary actuation, but to limit the structure which is secondarily actuated by targeting the structure in the suspension in closest proximity to the read/write heads.